NEW YORK - Roger Federer said he "beat myself" and "kind of self-destructed."

It was hard to argue after his earliest exit at the U.S. Open since 2003 - and it's becoming all too familiar.

Moved from Arthur Ashe Stadium to smaller Louis Armstrong Stadium due to a rain delay - Federer hadn't played there since 2006 - the Swiss looked out of sorts from the start against No. 19 seed Tommy Robredo.

"I struggled throughout, which is not very satisfying, to be honest," said five-time New York champion Federer, who hit 45 winners but also made 43 unforced errors. Worse, he was 2-for-16 on break points, 0-for-12 in the last two sets. "I mean, Tommy did a good job to keep the ball in play and make it difficult for me today."

At age 32, Federer has struggled with a bad back, and all along, he's had far more trouble winning matches than he usually does - particularly against the sort of players he barely broke a sweat against at his peak.

Robredo is one of them. Not only was Robredo 0-10 against Federer until Monday, he'd managed to win only three of the 27 previous sets they'd played. And his record in the fourth round of the U.S. Open was 0-7.

That Wimbledon loss ended a record run of reaching at least the quarterfinals at 36 consecutive Grand Slam tournaments.

It's the first year since 2002 Federer has gone through a full season without reaching a major final.

"It's been a difficult last three months," said Federer, who adjusted his schedule to get more matches under his belt and experimented with a larger racket after Wimbledon. "I just couldn't do it," he added. "It was a frustrating performance today."

Federer didn't blame the court switch or his lack of play on Armstrong.

"That's definitely the last excuse you could find," he said.

He insisted he was eager to get back to work and wasn't concerned that his anticipated clash with longtime rival Rafael Nadal would not materialize. Despite playing 31 times, they have never met at the U.S. Open.

"If I'm playing like this," said Federer, "I'm not going to beat Rafa, or (his opponent Philipp) Kohlschreiber, for that matter."

Robredo has been ranked as high as No. 5, albeit back in 2006, and this is his seventh trip to the quarterfinals at a major. He made it that far at this year's French Open by doing something no man had done since 1927, winning three matches in a row after dropping the first two sets of each.

Currently ranked No. 22, he will move inside the top 20 for the first time since 2010.

"For me, Roger for the moment is the best player of all times," Robredo said. "And to beat him in a huge stadium like the U.S. Open and in a Grand Slam, a match of five sets, it's like a dream, no?

"I am so, so happy. I am in quarterfinals again. It was a great day."

Federer has only one title in 2013, and he went through a stretch where he lost matches to three players ranked outside the top 50.

"I've definitely got to go back to work and come back stronger, you know, get rid of this loss now as quick as I can, forget about it, because that's not how I want to play from here on," Federer said. "I want to play better. I know I can. I showed it the last few weeks, that there is that level. So today was pretty frustrating."